Effect of alcohol on cellulose hydrolysis in super/subcritical alcohol-water mixtures

The focus of this work was on investigating the effects of different types of alcohol on the cellulose hydrolysis in supercritical/subcritical alcohol-water mixtures by selecting methanol, ethanol, and isopropanol as co-solvents. The experiments were conducted in a batch reactor under the following conditions: 5% mass ratio, 0.58 min reaction time and stirring speed 600 r/min. The experimental results showed that the reducing sugar yield was very low when the alcohol mole fraction in the alcohol-water mixture was more than 0.8, however, the yield turned very high when the mole fraction was less than 0.6. Critical parameters of alcohol-water mixtures revealed that the alcohol-water mixtures were in the supercritical state when the alcohol mole fraction was above 0.8 at 250°C. As a contrast, the mixtures were in the sub-critical state if the mole fraction turned into 0.6. Therefore, further investigations were carried out in sub-critical alcohol-water mixtures. It was found that ethanol was the best co-solvent among three kinds of co-solvents selected with respect to the yield of reducing sugar and the cost. The cellulose hydrolysis conditions in ethanol-water mixtures were optimized. The reducing sugar yield of cellulose hydrolysis was reached as high as 98.22% under the conditions of 0.22 mole fraction of ethanol, temperature of 260°C, pressure of 5.75MPa, reaction time of 0.58min, stirring speed of 600r/min, and the IR crystallinity index of cellulose was decreased from 0.618 to 0.211.